Electrical transformer with cooling means



Sept- 5, 1967 T. E. BASTls ETAL ELECTRICAL'TRANSFORMER WITH COOLING MEANS 4 Sheets-Sheet l Filed Sept. 30, 1964 INVENTRS THOMAS E. BAsT/s rHOWARD L BR/DGES G/LLETTE N HOUCK pom;-

Sepi- 5, 1967 T. E, BAsTls ETAL ELECTRICAL TRNSF'ORMER WITH COOLING MEANS 4 Sheets-Sheet Z3 Filed sept. 30, 1964 M sKM w C TGU A smo@ ARHM B.BNT. EL 50mm? ARTA/n MAE/ m THF/w Sept. 5, 1967 T, E; BAS-ns ETAL 3,340,489

ELECTRICAL TRANSFORMER WITH COOLING MEANS Filed Sept. 50, 1964 4 Sheets-Sheet 3 INVENTORS THOMAS E. eAsT/s HOWARD L. BRIDGES GILLETTE N. HOUCK w/LL/AM T MQORE Sept 5, 1967 T. E. BAS-ns ETAL ELECTRICAL TRANSFORMEH WITH COOLING MEANS 4 Sheets-Sheet 4 Filed sept. 5o, 1964 INVENTOR5 THOMAS E. EAST/S HOWARD L.. BRIDGES GILLETTE N- HOUCK WILL/AM 7T @OGRE ffy United States Patent O 3,340,489 ELECTRICAL TRANSFORMER WITH COOLING MEANS Thomas E. Bastis and Howard L. Bridges, Oakland, and Gillette N. Houck and William T. Moore, Lafayette, Calif., assignors to Kaiser Aluminum & Chemical Corporation, Oakland, Calif., a corporation of Delaware Filed Sept. 30, 1964, Ser. No. 400,453 15 Claims. (Cl. 336-61) The present invention relates generally to electrical transformers, and more particularly to encapsulated, drytype power transformers. v

Diiculty has been experienced in the past in winding transformers of the closed magnetic core type and in placing the windings, particularly the large number of turns primary winding, around the core. This dificulty is avoided in the transformer according to the present invention by placing the primary windings about sections of a tubelike casing and inserting magnetic core sections within the winding and casing sections, with the casing and core sections later assembled to form a closed core providing a complete magnetic circuit within a substantially tubular casing and with the primary winding therearound. With toroidal and other curved types of cores, the use of round magnet wire fails to take maximum advantage of the circumferential surface of the magnetic core at portions of larger radii, and further according to the present invention, the windings about the transformer core are preferably formed from a flat conductor which varies in width around the core, with the wider sections disposed upon core surfaces of greater radii to thereby make maximum use of the circumferential core surface.

Further in the manufacture of encapsulated, dry-type transformers, diiculty is experienced in extracting heat from the interior of the transformer, particularly where generated in the primary winding and in the core material. In the transformer according to the present invention, the magnetic core and the primary winding are successively encased, and flanges in the casings extend outwardly for connection to heat dissipating tins at the exterior of the transformer, thereby providing for more efficient dissipation of heat from the interior of the transformer and permitting its operation at higher power requirements for the same permissible temperature rise.

In the transformer according to the present invention, a substantially tubular casing is provided for the transformer core, and both the core and the casing are divided into complementary sections. The primary winding may be readily wound on a casing section by rotating the casing section about a diametrical or longitudinal axis while effecting circumferential oscillation thereof to distribute the primary winding over the casing section. The winding conductor has an insulating coating and is preferably dat and varies in width from a narrow section at the casing surface of minimum radius through tapered sections over radially extending surfaces to a wide section at the casing surface of greater radius, complementary core sections are placed in the wound casing sections and the casing and core sections are joined together to form a continuous magnetic path transformer core within a substantially tubular casing and with the primary windings thereabout.

The casing sections desirably have integral -flanges thereon adjacent their ends which are connected together and project outwardly for connection in good heat conducting relation to heat dissipating fins disposed at the exterior of the transformer casing. The outside of the primary winding is preferably enclosed in a second casing through which the flanges of the rst casing extend, and the casing for the primary winding also has llanges thereon which likewise extend outwardly for connection to heat disspating tins at the exterior of the transformer casing.

The secondary Winding for the transformer is desirably in the form of preformed straps of varying size, depending on the layer in which they are located, and transversely dimensioned similarly to the primary winding conductor to make optimum utilization of the peripheral dimensions available.

The casing flanges previously described are desirably connected edgewise in good thermal and electrical conducting relation to large heat radiating fins which are exposed at the exterior of the transformer casing. Electrical terminals may be provided on two of the outside ns to connect therethrough to the primary winding within the transformer. The secondary winding is connected to suitable terminals at the exterior of the transformer casing and the parts are electrically insulated by desired wire coatings and suitable plastic insulating or impregnating materials separating the various electrical elements within the transformer.

In addition to the above features, other objects and features of the invention will be apparent to those skilled in the art' from the following specification and the appended drawings, in which:

FIGURE 1 is a view, partly in section and partly in elevation, of an electrical power transformer according to the present invention;

FIGURE 2 is a horizontal sectional view through the transformer of FIGURE l FIGURE 3 is a detail view of several turns of the primary winding shown without the casing section on which they are wound;

FIGURE 4 is a detail view of a length of the conductor from which the primary winding is wound;

FIGURE 5 is a perspective View of the transformer core sections in exploded relation;

FIGURE 6 is a perspective view of a core casing section on which the primary winding is wound;

FIGURE 7 is an exploded perspective view showing the core and wound casing sections prior to final assembly;

FIGURE 8 is a perspective view of secondary winding turns shown without the transformer part about which they are wound;

FIGURE 9 is a view of secondary winding turns similar to FIGURE 8 but of a next adjacent layer;

FIGURE 10 is a perspective view showing the encased primary winding prior to the application of an insulating coating thereto;

FIGURE ll is a perspective view similar to FIGURE 10 and showing the straps of the first layer of the secondary winding being applied about the insulated casing; and

FIGURE 12 is a somewhat diagrammatic, perspective showing of the preformed straps for successive layers of the secondary winding. y

The embodiment of the present invention selected for illustration in the drawing employs a wound strip, toroidal core 21 disposed in an annular casing 22 about which a primary winding 23 is disposed. A partial casing 24 surrounds the primary winding 23 and about the casing 24 is disposed a secondary winding 25, all enclosed within an outer casing 26. The core casing 22 is provided with diametrically aligned stub flanges 2-7 and 28 to which are integrally connected, as by welding or brazing, large external heatradiating iins 29 and 31 in good thermal and I3 D electrical conducting relation. The enclosing casing 24 for the primary winding is provided with diarnetrically aligned stub flanges 32 and 33 integrally connected, as lby welding or brazing, to large external heat radiating ns 34 and 35 in good thermal and electrical conducting relation. The internal ends of the primary windings are connected to the casing 22 and electrical connection thereto is made through the fin 29 and stub flange 27 from an exterior primary terminal 36. The other ends of the primary windings are connected to the casing 24 and connection thereto is made from an exterior terminal 37 through the n 34 and stub ange 32. Terminals for the secondary output are indicated at 38 and are disposed within a cylindrical mounting throat 39 connected to the lower portion of the casing 2'6 and terminating in a flange 41 by which the transformer may be mounted.

Referring now to FIGURE 5, the transformer core 21 is illustrated as toroidal in form but features of the invention are equally applicable to transformer cores with other configurations. The toroidal shape shown in the drawings is desirably formed from a strip of grain oriented magnet steel wound upon itself into the form of an annular, flat coil. After the annular coil has been wound, two annular plates of insulating plastic material 42 and 43 are cemented tothe top and bottom of the core which is then cut along parallel planes at A and B to form the core sections 44 and 45 shown in FIGURE 5. The planes A and B are preferably substantially tangential tb the central opening in the annular core. The severed plates 42 and 43 are then drilled at their cut edges, as at 46, to receive dowel pins 47 to insure proper alignment of the core sections 44 and 45 so that the layers of the coil will match in perfect alignment to insure magnetic continuity across the faces of the core sections. It will be understood that screws may be located in previously drilled holes or other means used to insure the exact alignment of the cored sections for magnetic continuity across the section faces.

Prior to the segmenting or cutting operation on the core, it is desirably annealed, in accordance with standard metallurgical practices, and is covered with a resinous or plastic material to close all gaps or interstices between the layers of the core and in effect form a monolithic outer coating for the core which is numbered 48 in FIGURE 1. This coating may be applied in any desired manner, for example, by spraying, electrostatic application, or by dipping and sonically vibrating in order to effect uniform coating and elimination of all voids.

A core casing section 51 is illustrated in FIGURE 6 and may be a casting of a suitable metal, such as aluminum, which desirably provides both light weight and relatively high electrical and thermal conductivity. The casing 22 is illustrated as formed in two half sections 51, each of substantially 180 and of semi-circular, tubular form with end flanges 52, diametrically aligned and carrying the integral stub anges 27 and 28. The interior' wall of the tubular casing is provided with a slot 53 to provide a discontinuity in the casing path about the core 21 whereby the casing does not form a closed turn about the transformer core. Each casing section 51 is individually wound with a primary winding prior to the assembly of the casing sections. This may be done by rotating the casing section about an axis bisecting both of the stub flanges 27 and 28 so that the casing section rotates continuously through 360 about this diametrical axis, and at the same time the section is desirably shifted or oscillated circumferentially to distribute the primary winding over the entire circumferential length of the section.

A length of primary magnet wire which it is preferred to use is illustrated at 54 in FIGURE 4, and in coiled form in FIGURE 3. This primary conductor is formed of a good conducting material, such as aluminum or copper having an insulating covering. The conductor is desirably of repetitive shaping to place a narrow length against the central opening surface, tapered length at the top and bottom of the casing, and a wide length across the outer surface of the casing. The conductor 54 has flat opposite surfaces and includes a narrow length 55, an outwardly tapering length 56, a wide length 57 and an inwardly tapering length 58 which connects to the next succeeding narrow length 55, with the conductor repeating the shaped lengths for the entire length thereof required to complete one layer of the primary winding. T he next layer of the primary winding uses similar narrow, tapered and wide lengths, but the longitudinal dimensions thereof are increased somewhat to laccommodate the increased spiral length in which they are wound. Likewise, additional layers use the same combination of narrow, tapered and wide conductor lengths, but the longitudinaal dimensions of the lengths increase for successive layers of the winding.

In winding the primary windings on the casing sections 51, the starting end of each primary winding is spot welded or otherwise secured to the section on which it is to be wound which thereby becomes the -terminal for that end of the primary winding. While the conductor 54 has an insulating coating, additional insulation may, if desired, be placed between successive winding layers in accordance with conventional transformer winding practice.

The wound core casing sections are then in the form shown in FIGURE 7, which also shows the core sections 44 and 45 inserted within the casing sections 51 in the manner shown in FIGURE 7. The two wound casing sections are then Abrought together to mate their flanges 52 and the stub flanges 27 and 28, the dowel pins 47 being received in the holes 46 in the plastic plates 42 and 43 so as to align the layers or turns of the core sections 44 and 45 to secure magnetic continuity lacross the faces of the core sections, with the flux lines in each individual core layer continuing across the section ends into the same layer in the mating section. The anges 52 and stub flanges 27, 28 are desirably integrally secured together, as by welding or brazing.

The assembled core, core casing and primary winding are now enclosed in the casing 24, as shown in FIGURE 10, with the stub flanges 27 and 28 insulated from the casing 24. The casing 24 is made up of two generally cup-shaped halves 61 and 62 having integral flanges 32 and 33 projecting therefrom and central openings uncovering the opening through the core. The ends of the primary windings 23 opposite to the ends electrically connected to the casing 22 are now electrically connected to the casing 24 which, with its anges 33, 34, thereby forms an opposite terminal for the primary winding. The stub anges 27 and 28 are provided with an insulating coating and extend through clearance slots 63 in the casing 24.

After the halves 61 and 62 of casing 24 have been assembled about the Iprimary winding 23, this sub-assembly is given a heavy coat of insulation 60, such as a heavy silicone, by spraying, dipping or injection molding and thereafter vulcanizing and curing the coating. This coating advantageously serves to insulate the primary winding from the secondary winding to lbe applied thereover.

The secondary winding 25 is then applied about the insulated casing 24 in the form of individual straps 50 such as are more or less diagrammatically illustrated in FIGURE 12. The set 64 of straps 50 forms the first layer next to the insulation 60 and the sets of straps 65, 66 and 67 forming successive layers thereover. The individual straps are generally U-shaped, as illustrated, with bights 68, outer legs 69 and inner legs 71, and are placed about the casing 24 in the manner illustrated in FIGURE 1l.

The straps 50 have their bights 68 tapered, as illustrated, and the inner legs 71 of lesser width than the outer legs 69, thus conforming to the available inner and outer circumferential widths. The ends of the wide outer legs 69 are notched at 72 to receive tongues 73 at the ends of the legs 71 of adjacent straps, the ends of the legsv69 and 71 being bent around the top and bottom of casing 24 as shown at 74 in FIGURES 8, 9 and 11. The tongues 73 are welded in the notches 72 to join the end of one strap to the end of the next `adjacent strap to form the winding turns. The straps 50 are coated with suitable insulation exposing only the parts thereof which are to be welded together to form the electrical circuit. In the forepart of FIGURE 11 the straps 50 are shown bent over at 74 and with the tongues 73 welded in the notches 72. At the back of FIGURE l1 the straps 50 are shown mounted on the casing but before bending of the strap ends across the casing into interconnected relation.

It will be seen that each successive set of straps 65-67 is larger than the preceding so that the layers of the secondary winding will be received over each other with the straps of each layer properly enclosing the preceding layer and nesting within the succeeding layer. The ends of the secondary winding and a mid-point thereon are desirably connected to the terminals 38 so as to provide for connection to a 1Z0-240 volt system.

With the completion of the secondary winding, the large exterior flns 29, 31 and 34, 35 are butt Welded, brazed or otherwise connected to theA ends of the stub flanges 27, 28 and 32, 33, respectively, in good electrical and thermal conducting relation. The entire transformer, including the exterior fins, is now given a final coating of insulation 75 which may be of the heavy silicone insulation previously described, vulcanized and cured in place. The transformer is completed by assembling sections76 and 77 of outer casing 26 thereabout, the sections being provided with suitable notches 78 through which the exterior fins extend. The outer casing sections 76 and 77 may then be welded or brazed together at their joints. The outer casing is provided with mounting brackets 79 by which it may be side mounted, or the transformer may be bottom mounted by the flange 41.

The connection of the fins 29 and 31 to the flanges 27 and 28 of casing 22, and 34, 35 to the flanges 32 and 33 of casing 24 provides for efiicient heat transfer from inside of the transformer to the large exterior fin surfaces from which the heat may be dissipated to the ambient. This enables the transformer to be operated at higher power output for a given temperature limit, or conversely, at a cooler temperature for a given power output. The outward transfer of interiorly generated heat is aided yby the form of the secondary winding straps wherein the wide outer legs 69 are relatively cool and form a heat sink for the flow of interior heat thereto and from which heat is conducted to the outer casing 26 for dissipation into the ambient directly therefrom. The fins 29 and 34 also provide convenient means for the connection of the primary lines to terminals 36 -and 37 thereon, thereby connecting through the fins and the casings 22 and 24 to the primary windings 23.

While a certain preferred embodiment of the present invention has been specifically illustrated and described, it will be understood that the invention is not limited thereto as many variations will be apparent to those skilled in the art and the invention is to be given its broadest interpretation within the terms of the following claims.

What is claimed is:

1. An electrical power transformer comprising: a pair of complementary sections assembled to provide a magnetic core forming a continuous magnetic circuit with a central opening accommodating the trans-former windings; a substantially tubular casing made up of sections of electrical and thermal conducting material assembled and shaped to substantially enclose said magnetic core while retaining said central opening for the reception of the windings, said core and casing sections mating as subassemblies whose assembly results in a continuous magnetic core with a substantially Itubular casing; primary transformer windings disposed about said casing sections while separated; secondary transformer windings disposed about said core, casing and primary windings; a flange on said casing extending to the exterior of said secondary windings; a heat dissipating fin connected to said flange in good heat conducting relation; means connecting said primary windings -to said casing; a primary terminal mounted on said fin to connect to the primary windings through the fin, flange and casing; a second casing substantially enclosing said primary windings, first casing and core; means connecting said primary windings to said second casing; a flange on said second casing extending to the outside of said secondary windings; a heat dissipating fin connected to said second casing in good electrical and heat conducting relation; and a second primary terminal on said second fin connected to the transformer windings through said second fin and flange on said second casing.

2. An electrical power transformer comprising a plurality of complementary sections assembled and mated together to form a closed magnetic core provided with a central opening therethrough for receiving the primary and secondary windings of the transformer, the opposing and mating ends of the complementary sections of the core being located in planes arranged substantially tangential to the central opening of the core; pin type means for aligning and holding said core sections together; a substantially tubular 'and sectionalized casing substantially surounding the core; a primary winding disposed about said core and casing, said primary winding comprising a length of conductor wire having repetitive alternate narrow and wide portions, the wide portions of the wire being disposed about the casing surface of greater radius and the narrow portions of the wire being disposed about the casing surface of minimum radius; a second substantially tubular casing disposed about said core said first casing and said primary winding and a secondary winding disposed about said second casing; said secondary winding comprising at least one set of straps, the one terminal end of each strap in said set of straps being notched while the opposing terminal end of the said strap has a tongue and the `straps in the set of straps being so arranged on the second casing whereby the tongue on one strap is disposed within the notch of the next adjacent strap.

3. A transformer as set forth in claim 2 wherein said first casing is provided with radially disposed flanges extending to the exterior of the secondary winding, and said second casing being provided with slots through which the flanges of the first casing protrude and with radially disposed flanges also extending -to the exterior of the secondary winding.

4. A transformer as set forth in claim 2 wherein said first casing is provided with radially disposed flanges extending to the exterior of the secondary winding; said second casing is provided with slots through which the flanges of the first casing protrude and with radially disposed flanges also extending to the exterior of the secondary winding and heat dissipating fins attached to the said flanges of the first and second casings.

5. A transformer as set forth in claim 2 wherein said first casing is provided with radially disposed flanges extending to the exterior of the secondary winding; said second `casingr is provided with slots through which the flanges of the first casing protrude and with radially disposed flanges also extending to the exterior of the secondary winding; heat dissipating fins atached to the flanges of the first and second casings and a final outer casing enclosing said core said first and second casings and said primary and secondary windings, said final outer casing having slots through which the flanges on said first and second casings protrude.

6. An electrical power transformer comprising: a flat coil of magnetic strip forming the transformer core; an insulating cap mounted on each side of said coil, said core and caps being comprised of complementary sections assembled together to form a closed and capped core provided with a central opening; a tubular casing made up o'f sections assembled to substantially enclose the core and caps; indexing means between the faces of said cap sections and joining the core and cap sections together to mate the coil turns of the core across the faces of the sections and to form a continuous magnetic circuit within the casing and with the casing having a central opening corresponding to the central opening through the core; primary transformer coils disposed about said casing sections and electrically connected to said sections which thereby become one terminal therefor; exteriorly extending flanges on said casing; a second casin-g enclosing at least the outer portions of said primary coils and first casing and connected to said primary coils to form the other terminal therefor; flanges extending outwardly from said second casing; a secondary transformer winding disposed about said second casing and insulated therefrom; and primary terminals connected separately to the flanges on said first and second -casings to energize the primary transformer coils.

7. An electrical power transformer comprising: a flat coil of magnetic strip forming the transformer core; an insulating cap mounted on each side of said coil, said core and caps being comprised of complementary sections assembled together to form a closed and capped core provided with a central opening; a tubular casing made up of sections assembled together to substantially enclose the core and caps; indexing means between the faces of said cap sections and joining the core land cap sections together to mate the coil turns of the core across the faces of the sections and to form a continuous magnetic circuit within the casing and with the casing also having a central opening corresponding to the central opening through the core; primary transformer coils disposed about said casing sections and electrically connected to said sections which thereby become one terminal therefor; exteriorly extending flanges on said casing; -a second casing enclosing at least the outer portions of said primary coils and first casing and connected to said primary coils to form the other terminal therefor; flanges extending outwardly from said second casing; a secondary transformer winding disposed about said second casing and insulated therefrom; heat dissipating fins connected to said casing flanges in good electrical and heat conducting relation, the fins and flanges of each casing being electrically insulated from the fins and flanges of the other; and primary terminals connected individually to a fin of each casing to energize the primary coils.

8. An electrical power transformer comprising a plurality of complementary sections assembled and mated together to form a closed magnetic core provided with a central opening therethrough for receiving the primary and secondary windings of the transformer, the opposed and mating ends of the complementtary and mated sections of the core being located in planes arranged substantially tangential to the central opening of the core; interengaging means associated with said sections for aligning adjoining sections of said core in face-to-face abutting engagement, a tubular casing surrounding the central opening, said casing including a plurality of complementary sections, each casing section receiving one of the core sections and having one of the mating ends of the core section extending outwardly therefrom into the complementary casing section; means interconnecting said casing sections and holding the mated ends of the core sections in contact in order to establish a continuous flux path across the interfaces of adjoining sections of said core and thus circumferentially thereof, said interengaging means being displaced from the end edges of adjoining sections and thus being outside of said flux path; and electrical winding means for establishing magnetic flux in said core along said flux path.

, 9. In an electrical transformer as set forth in claim 8 in which said interconnecting means is comprised of flanges disposed at the ends of each section of said casing.

10. In an electrical transformer as set forth in claim 8 further including insulating means disposed about said sections of said core so as to electrically separate said core from said casing.

11. In an electrical transformer as set forth in claim 10 in which said interengaging means are disposed in said insulating means relative to the opposite end edges of adjoining sections of said core, the opposite end edges of adjoining sections and said interengaging means associated therewith being located in separate intersecting planes angularly disposed relative to each other at an angle less than wherein the opposite end edges of adjoining sections of said core are located in one of the intersecting planes arranged substantially tangential to the opening of said core.

12. In an electrical transformer as set forth in claim 8 in which said winding means are wound around said casing, a second casing including slots therein to substantially enclose said winding means wound about said first casing, a first series of flanges aflixed to said first casing and extending through the exterior -of said windings and through the slots provided in said second casing, a second series of flanges aflixed to the exterior of said second casing and disposed in interdigitated relation relative to said first series of flanges, said first and second series of flanges being electrically connected to said windings to provide terminal connections thereof.

13. An electrical power transformer comprising a plurality of complementary sections assembled and mated together to form a closed magnetic core provided with a central opening therethrough for receiving the primary and secondary windings of the transformer, the opposing and mating ends of the complementary and mated sections of the core being located in planes arranged substantially tangential to the central opening of the core; pin type means for aligning and holding said core sections together; a substantially tubular and sectionalized casing substantially surrounding and enclosing the core, said casing being provided with radially disposed flange elements, a primary winding disposed about and adjacent to said casing, a second casing also provided with radially disposed flange elements and clearance slots through which the flange elements of the first casing extend and a secondary winding disposed about and adjacent to the second casing.

14. An electrical power transformer comprising a plurality of complementary sections -assembled and mated together to form a closed magnetic core provided with a central opening therethrough for receiving the primary and secondary windings of the transformer, the opposed and mating ends of the complementary and mated sections of the core being located in planes arranged substantially tangential to the central opening of the core; pin type means for aligning and holding said core sections together; a substantially tubular casing made up of sections provided with flanges, said sections being assembled to substantially surround and enclose said core without closing off the central opening of the core; primary and secondary windings disposed about said core and casing, said flanges on said casing sections extending through said windings to transfer outwardly heat generated within the interior of the transformer and heat dissipating fins attached to said flanges of said first casing.

15. An electrical power transformer comprising a plurality of complementary sections assembled and mated together to form a closed magnetic core provided with a central opening therethrough for receiving the primary and secondary windings of the transformer, the opposed and mating ends of the complementary and mated sections of the core being located in planes arranged substantially tangential to the central opening of the core; pin type means for aligning and holding said core sections together; .a substantially tubular casing made up of sections, said sections being assembled to `substantially surround and enclose said core Without closing 01T the central opening of the core; said casing being provided with radially disposed flange elements, a primary Winding disposed about and adjacent to said casing, ra second casing also provided with radially disposed flange elements and clearance slots through which the ange elements of said rst casing extend, a secondary Winding disposed about and .adjacent to the second casing and heat dissipating ns attached to said ange elements of said second casing.

References Cited UNITED STATES PATENTS Berry 336-212 X Bowman 336-216 X Melville 336-61 Fredrickson 336-212 Remenyil 336-61 Peabody 336-229 Helberg 336-192 Halaeoy 336-229 X LEWIS H. MYERS, Primary Examiner. T. J. KOZMA, Assistant Examiner. 

13. AN ELECTRICAL POWER TRANSFORMER COMPRISING A PLURALITY OF COMPLEMENTARY SECTIONS ASSEMBLED AND MATED TOGETHER TO FORM A CLOSED MAGNETIC CORE PROVIDED WITH A CENTRAL OPENING THERETHROUGH FOR RECEIVING THE PRIMARY AND SECONDARY WINDINGS OF THE TRANSFORMER, THE OPPOSING AND MATING ENDS OF THE COMPLEMENTARY AND MATED SECTIONS OF THE CORE BEING LOCATED IN PLANES ARRANGED SUBSTANTIALLY TANGENTIAL TO THE CENTRAL OPENING OF THE CORE; PIN TYPE MEANS FOR ALIGNING AND HOLDING SAID CORE SECTIONS TOGETHER; A SUBSTANTIALLY TUBULAR AND SECTIONALIZED CASING SUBSTANTIALLY SURROUNDING AND ENCLOSING THE CORE, SAID CASING BEING PROVIDED WITH RADIALLY DISPOSED FLANGE ELEMENTS, A PRIMARY WINDING DISPOSED ABOUT THE ADJACENT TO SAID CASING, A SECOND CASING ALSO PROVIDED WITH RADIALLY DISPOSED FLANGE ELEMENTS AND CLEARANCE SLOTS THROUGH WHICH THE FLANGE ELEMENTS OF THE FIRST CASING EXTEND AND A SECONDARY WINDING DISPOSED ABOUT AND ADJACENT TO THE SECOND CASING. 